Nah, it's most likely as I said above back in January but never received a reply... @3x is css media query talk for mobile phone 'retina displays' with a pixel ratio (aka scaling factor) set at 3, ie a phone with a 2560 x 1440 pixel QHD resolution (samsung s6) which has a pixel ratio set at 3 would show a website as if it's on a '853 x 640' screen. The iphone retina used @2x, @3x and even @4x is for even higher resolutions screens.